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Can someone explain to an EE how I would go about measuring the thermal properties of a material? I need to measure the thermal impedance, expansion, and conductance (k) of an epoxy, and the manufacturer has not done those measurements. I'd like to be able to do it without any fancy equipment either. Literally something I can do in the garage and calculate the results. It doesn't have to be THAT accurate, but as close as can be. I do have some equipment at my disposal, but nothing designed for this task.

Edit - Perhaps a better way to ask the question is this: How can I determine from a material with no known properties, how well I can dissipate heat through a specified volume? Is the Guarded hot plate method acceptable? I've read about it a little, but I'm not fully certain as to how it should be properly conducted.

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  • $\begingroup$ Thermal impedance is a property of a structure. There's no such thing as thermal impedance of epoxy. A built block which contains known materials and has known dimensions can have thermal impedance which can be calculated or measured. In theory thermal impedance could be defined as a property of material if one tries to combine the heat capacity and heat conductivity to frequency dependent complex impedance in the way how the impedance of a material can be built in electromagnetics. I have never seen such attempts. $\endgroup$
    – user50879
    Commented Aug 28 at 11:58
  • $\begingroup$ Thanks @user50879 - I edited my post with a further clarification. Does that make the question any easier to answer? $\endgroup$
    – Jedi Engineer
    Commented Aug 28 at 14:56

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If you succeed to construct a constant temperature hot plate placed against a constant temperature cold plate and there's a known (thickness, area, material) between the plates and you can measure the heating power to keep the hot plate in the wanted temperature you can get a good estimate for the thermal resistance between the plates. That, of course assumes the temperatures really are kept constant and there's no remarkable heat leaks from the hot plate to elsewhere than to the cooled cold plate.

Heat leaks to sideways, of course, can be taken into the account by calibrating and it's possible to use warming or cooling rates as the basement of the measurements, but all that generates complex new calculation needs.

Thermal expansion of a solid material can be measured if you can measure very short distance changes (mechanical micrometer, laser interferometer) The common temperature meter principle could be used for liquids. Ability to control the temperatures is a must. The old controlling method was to use boiling water and melting ice. They work also today if the materials can stand zero and 100 degrees centigrade and you know how your measurement equipment get affected.

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  • $\begingroup$ Thanks! Could you edit to include an equation for k that doesn't rely on heat flow? $\endgroup$
    – Jedi Engineer
    Commented Aug 30 at 11:22

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